mutter/src/tests/clutter/conform/scripts/test-script-timeline-markers.json

{
  "id" : "timeline0",
  "type" : "ClutterTimeline",
  "duration" : 1000,

  "markers" : [
    { "name" : "marker0", "time" : 250 },
    { "name" : "marker1", "time" : 500 },
    { "name" : "marker2", "time" : 750 },
    { "name" : "marker3", "progress" : 0.5 }
  ]
}